This application claims the benefit of German Patent Application No. 101 06 093.9-12 entitled xe2x80x9cVerbindungselement rnit einer Schraube und einem daran unverlierbar angeordneten Sxc3xctutzelementxe2x80x9d, filed on Feb. 8, 2001.
The present invention generally relates to a screw connector including a screw and a work supporting element being captively connected to the screw. More particularly, the present invention relates to a special design of the thread runout of the screw facing the head of the screw.
Screw connectors including a screw and a work supporting element being captively connected to the screw to prevent unintentional detachment of the two elements are produced in series to attain a great pre-production level, and to simplify assembly of the screw connectors. The screw connectors serve to connect components.
A screw connector is known from German Patent Application No. 199 24 502 A1. The known screw connector that functions as a connecting element includes a screw having a head with a head Supporting surface and a shank and a support sleeve that surrounds the shank of the screw and functions as a supporting element. The shank includes a cylindrical shank portion and a threaded portion. The shank portion faces towards the head of the screw, while the threaded portion is more or less located at the free end of the shank of the screw facing away from the head. The threaded portion may also be arranged in a middle region of the shank, for example in the case of the screw at its free end including a centering element.
The support sleeve functions as a supporting element and may be designed as a bush or as a plain washer. The supporting element may also include more of such supporting elements. The supporting element includes a narrowing location having a diameter which is less than the outer diameter of the thread of the threaded portion of the screw. The narrowing location may be produced in different ways, for example by impressions being located on the circumference of the bush, or by a continuous protrusion protruding towards the inside. It is also possible to use separate elements, for example a securing ring, being located in the inner diameter of the bush. When a plain washer is used as the supporting element, the bore of the plain washer forms the narrowing location. In this way, the bore forms a continuous enlarging element protruding towards the inside.
The shank portion of the screw has a comparatively reduced diameterxe2x80x94meaning a diameter which is less than the outer diameter of the thread being located on the threaded portion. The reduced diameter of the shank portion may correspond to the rolling diameter of the screw during its manufacture.
When a thread is to be produced on the shank of a screwxe2x80x94especially by rollingxe2x80x94this is only possible by producing a thread runout facing the head of the screw. The diameter of the thread convolution (or of the thread convolutions) increases in the region of the thread runout facing the head of the screw from the rolling diameter, for example, to the outer diameter of the thread in the threaded portion being located adjacent to the runout. Standardization of the thread runout differentiates between a xe2x80x9cstandard casexe2x80x9d and a so called xe2x80x9cshort designxe2x80x9d. In the standard case, the thread convolution extends about 2.5 rotations of the screwxe2x80x94meaning about 900xc2x0xe2x80x94while changing its outer diameter. The short design of the thread runout relates to 1.25 rotationsxe2x80x94meaning 450xc2x0. Even shorter thread runouts would be theoretically possible, but their production is expensive due to comparatively reduced usable times of the tools for rolling these threads.
In the prior art, in the region of each thread runoutxe2x80x94no matter whether in the standard case or in the short design casexe2x80x94there is a conical surrounding cone at the screw, the surrounding cone contacting the narrowing location of the supporting element. When one imagines winding down the thread convolution of the thread runout, one attains a very long inclined plane with a slowly increasing angle of inclination. The surrounding cone and the inclined plane, respectively, have the effect of the danger of the supporting element getting clamped in the region of the thread runout.
Such known connecting elements are especially used as bulk goods at assembly stations. Usually, a feeding apparatus and a conveying apparatus, respectively, are prearranged to the assembly station, the feeding apparatus ensuring that the connecting elements are located in a row, for example. Such conveying apparatuses often use vibration drives. Using vibration drives, there is the danger of the supporting element being vibrated in a way that it is located on the screw too fixedly such that it can no longer be assembled in the assembly station. Even in case such known connecting elements are separately fed to reach their desired place of application, there also is the danger ofxe2x80x94at least in some of the connecting elementsxe2x80x94the supporting element in the region of the thread runout having a clamped seat at the screw during transportation of the known connecting elements as bulk goods. These disadvantages do not only occur when the narrowing locations are designed as impressions being located at the supporting element in a spaced apart manner, but also when the narrowing locations are designed to be continuous over the circumference of the supporting element. In case of using local impressions, there is the danger of these impressions being vibrated and clamped in the position in which they engage two adjacent portions of the thread convolution in the region of the thread runout facing the head of the screw.
The present invention relates to a screw connector that functions as a connecting element, including a screw including a head and a shank and a supporting element that surrounds the shank of the screw and functions as a work supporting element.
The shank of the screw has an end remote from the head, and the shank includes a shank portion adjacent the head, a threaded portion more or less remote from the head and an increasing element formed as an inclined step that functions as a stop between the shank portion and the threaded portion. It is to be understood that the thread of a screw always has two ends or runouts, one of them facing the free end of the screw, and the other one facing the head of the screw. The present invention relates to the design of the end of the thread facing the head of the screw.
The threaded portion of the screw has an outer diameter, and it includes a thread runout facing the head of the screw and extending from the thread to the shank portion of the screw. The thread runout has an axial extension and a circumference. The shank portion has a diameter which is less than the outer diameter of the threaded portion. The step is produced by removing at least a portion of the thread runout at least over a part of the axial extension and of the circumference of the thread runout in a way that the step has a an outer diameter which approximately corresponds to the outer diameter of the threaded portion.
The screw connector also includes a work supporting element that is captively connected to the screw and includes a narrowing location facing the shank of the screw having a diameter which is less than the outer diameter of the threaded portion of the screw.
The present invention also relates to a connecting unit including a screw including a head and a shank. The shank has an end, and it includes a shank portion, a threaded portion and a stop element. The threaded portion has an outer diameter, and it includes a thread end facing the head. The thread end has an axial extension and a circumference. The shank portion has a diameter which is less than the outer diameter of the threaded portion. The stop element is produced by removing the thread runout at least over a part of the axial extension and of the circumference of the thread runout in a way that the stop element is formed with has a an outer diameter which approximately corresponds to the outer diameter of the threaded portion, and that the screw in the region of the removed thread end has a surrounding diameter which has an approximately cylindrical shape and which is less than the diameter of the narrowing location.
The connecting unit further includes a work supporting element being connected to the screw and the supporting element includes a narrowing location having a diameter which is less than the outer diameter of the threaded portion. The narrowing location is designed and arranged to cooperate with the stop element to prevent unintentional removal of the supporting element from the screw.
With the novel connecting element, the tendency of clamping effects acting between the screw and the supporting element are substantially reduced, especially when automatically conveying the connecting element. Usually, the screw and the supporting element are made of metal. However, different materials, for example plastic material, may also be used for the novel connecting element.
In the novel connecting element, the thread runout, orxe2x80x94in other wordsxe2x80x94the end of the thread facing the head of the screw, is at least partially removed. It may also be completely removed. In this way, the surrounding cone shape of the thread runout in this region is eliminated, and the thread runout is deformed to have the shape of a surrounding cylinder. It is desired to produce an increasing element shaped as a step or a stop at the beginning of the threaded portion facing the head of the screw. The novel inclination element serves as a stop for the narrowing location being located at the supporting element. The stop is effective as it prevents movement of the supporting element about the shank and threads in an axial direction off the end of the screw, and possibly also in a tangential direction. In the region of the step, the diameter of the screw increases in a tangential direction. However, this increase in diameter takes place over a comparatively shorter length than it is known in the prior art. For example, the increase in the outer diameter of the thread convolution at the intersecting surface of the step with the flank of the thread convolution only extends over a fraction of one rotation of the screw.
In this way, there is a sudden transition between the shank portion and the threaded portion of the screw in an axial direction and in a tangential direction This sudden transition strongly reduces and eliminates, the tendency of the support sleeve getting clamped in the threads of at the screw. This especially applies when the support sleeve is located at the screw to be rotatable about the shank of the screw.
The thread runout may be entirely or partly reduced by removing material or without removing material. Especially, it is possible to produce the novel runout by rolling. In this way, the outer diameter of the thread runout is reduced by rolling it flat. Usually, there is a remainder of the thread runout. However, the remainder is at least approximately surrounded by the imaginary surrounding cylinder. However, the remainder of the thread runout is small and cannot cause clamping of the supporting elements during movement of the supporting element with respect to the screw.
It is especially preferred to design the screw such that it has a surrounding diameter which is axially cylindrical in the region of the thread runout facing the head of the screw. However, the screw may also be designed in a way that the thread runout ends in a slightly conical surrounding diameter since different amounts of material have to be rolled down over the axial length of the thread runout. It is desired to chose the design such that there is no clamping contact with respect to the narrow location or to the narrow locations of the supporting element. The beginning of the thread (or in other words, the end of the thread facing the head of the screw) includes a contact surface or a supporting surface in the form of a step. The step substantially extends in a radial direction, it is substantially effective in an axial direction, and it only covers part of the circumference of the screw. The step also has an arcuate surface extending in a tangential direction. However, this does not have a negative effect in combination with the design of the supporting element. This is especially preferred when the surrounding diameter or the surrounding cylinder of the supporting element is substantially less than the diameter of the narrow location. It is preferred to chose an arrangement allowing for increased play or clearance to securely prevent the tendency of clamping effects. On the other hand, it is preferred that the surrounding diameter of the supporting element is morexe2x80x94but especially only slightly morexe2x80x94than the reduced diameter of the shank portion.
A design of the step at the beginning of the remainder of the thread of the threaded portion in which the step is rather big and in which the step starts suddenly is advantageous. The preferred design is to arrange the step at the place where the thread runout is connected to the thread portion. However, the step may also be arranged in the beginning portion of the thread portion, it is possible to arrange the step within the primary thread runout such that the step itself is located on a comparatively smaller outer diameter compared to the outer diameter of the thread of the threaded portion.
In all cases, it is preferred that the novel screw includes a stop or an inclination element which extends over a part of the circumference, and which cooperates with the narrowing location of the supporting element in an axial direction.
The increasing element or step may be designed and arranged to cover less than approximately 180xc2x0 of the circumference of the thread runout. Preferably, the step is designed and arranged to cover approximately 90xc2x0 of the circumference of the thread runout. When the step is designed to extend in a radial directionxe2x80x94meaning a direction perpendicular with respect to the longitudinal axis of the screwxe2x80x94there is a sectional surface of the surrounding cylinder with respect to the respective thread convolution of approximately 90xc2x0 of the circumference. The thread convolution of the thread runout or of the thread is not removed in this region. Consequently, the outer diameter increases and enlarges in a tangential direction. In the case of threads including a plurality of convolutions, there is a plurality of smaller sectional surfaces. The remainder of the inclined thread convolution of the thread runout preferably extends over less than 180xc2x0.
The thread runout of the threaded portion of the screw may be produced by removing material or without removing material. It is especially advantageous to roll the thread runout facing the head of the screw down to the rolling diameter of the shank portion. Rolling means that masses only have to be deformed and moved instead of being removed. Consequently, when great deformation is desiredxe2x80x94especially when deforming the screw to reach the rolling diameter or even less than the rolling diameterxe2x80x94the length of the screw is increased. However, there are no negative effects. In the case of removing materialxe2x80x94for example by turning on a lathe or by grindingxe2x80x94it is easily possible to reduce the diameter to reach the rolling diameter. When the screw is deformed by cold forming without removing chips, it is even possible that the screw in the region of the removed thread runout includes an enlarged portion formed by rolling. In this case, the enlarged portion functions as the counter supporting surface for the narrow locations of the supporting element. In this way, they form the increasing element being arranged in the region of the thread runout instead of at its end. However, the attained effect is similar to the above described constructions. The continuous enlarging element may also be produced by removing chips.
When the supporting element is designed as a bush, the inner diameter of the bush may be more than the outer diameter of the threaded portion. A plurality of impressions may be located about the circumference of the bush in a spaced apart manner, as it corresponds to the number of convolutions of the thread. Usual threads only include one convolution. However, screws including threads having more than one convolution are also used in the art. The number of spaced apart impressions preferably is more than the number of convolutions of the thread to ensure that at least one of the impressions contacts the step in each relative position between the supporting element and the screw. When the step extends over approximately 90xc2x0 of the circumference, it is preferred to use at least five impressions spaced apart about the circumference. When the step extends over approximately 180xc2x0 of the circumference, it is preferred to use at least three impressions spaced apart about the circumference to ensure that at least one impression contacts the step in all relative positions.
When the supporting element is designed as a plain washer, the plain washer may have an inner diameter which is less than the outer diameter of the threaded portion to form the narrowing place In such a case, it is not necessary to arrange separate impressions or other counter surface elements.
There are a number of different possibilities of arranging the step-like increasing element. The design may be chosen in a way that the increment of the surrounding diameter towards the outer diameter of the threaded portion is located in the region of the threaded portion. The step-like increasing element may also be located at the transition location between the thread runout and the thread of the threaded portion. Furthermore, it is possible to chose the thread runout to have a comparatively shorter axial extension.